1. Field of the Invention
The invention relates to an electronic control unit and a communication unit capable of connecting a plurality of communication networks formed in a vehicle with each other, and a communication system connected with the electronic control unit and the communication unit and to a method.
2. Description of the Related Art
Known communication systems have a plurality of electronic control units (ECUs) for controlling parts of a vehicle. The ECUs are connected via a communication bus to enable mutual data communication. Cooperation control among the ECUs of such a communication system has become easier in recent years with the multiplexing and speeding-up of vehicle communication. Specifically, it became possible to connect many ECUs with one communication bus to increase the number of combinations of ECUs for data transfer.
The known communication system described above is separated into a plurality of communication buses and these communication buses are connected via a relay device, such as a gateway to form a multiplexed communication system (see, for example, Japanese Unexamined Patent Publication No. 2000-78179, Japanese Unexamined Patent Publication No. 2003-17581 and Japanese Unexamined Patent Publication No. 2002-271994).
Japanese Unexamined Patent Publication No. 2000-78179 and Japanese Unexamined Patent Publication No. 2003-17581 disclose an electrical connection box capable of connecting a plurality of communication networks. According to these documents a gateway circuit connects a plurality of communication networks with the electrical connection box. Thus, communication is conducted by one relaying by the electrical connection box without via another wiring harness even if the protocols of units connected with a wiring harness connected with the electrical connection box differ and communication is conducted among these units.
Japanese Unexamined Patent Publication No. 2003-17581 also discloses a construction enabling CAM communication between the communication bus and the electrical connection box by providing the electrical connection box with a CAN communication function as an automotive communication protocol.
However, the following problem was present in the case of utilizing the electrical connection boxes disclosed in the above documents as a relay device of a multiplexed communication system for vehicle. Specifically, in the multiplexed communication system for vehicle, a relay device, which was unnecessary at an initial stage of development, may possibly become necessary at a later stage of development or conversely a relay, which was necessary at an initial stage of development, may possibly become unnecessary at a later stage due to an increase or decrease in the number of ECUs, a revision in communication specifications during the development of the communication system.
If a new relay device becomes necessary at the later stage of development, there is no place for installing the new relay device in many cases. Even if an installation place could be ensured, the communication bus and the wiring harness including the communication bus need to be laid again, with the result that the installation of the new relay device is often difficult.
On the other hand, if the relay device becomes unnecessary at the later stage of development, wires and an installation place for the relay device may be wasted. Particularly, in the case of incorporating the relay device into an ECU having another function for cost reduction or other reason instead of realizing the relay device as an independent device, the relay device is wasted without being used, which increases cost.
In view of the above problems, an object of the present invention is to provide an electronic control unit, a communication unit and a communication system and method capable of preventing an increase in development cost resulting from the addition or deletion of a relay device even in the case of an increase or decrease in the number of ECUs, a revision in communication specifications or the like during the development of the communication system.